152 



I>K"<EE1>INGS OF THE AMERICAN ACADEMY. 



circuit reaches 98 per cent of its maximum strength in about gths of 

 a second less time than when the secondary La closed. In this case the 

 final current was 2. .so amperes. Of course the degree of divergence of 

 the current curve for the primary circuit when the secondary is closed, 

 from the corresponding curve when the secondary is open, depends 

 very much upon the number of turns of the secondary and upon its 

 resistance. 



SECONDS. 



Figihi: 4"). 



Reverse current curves for the coil of 2788 turns belonging to the magnet Q, 

 when the circuit of a secondary coil of 10'J"> turns was closed ( C) ami open (/')■ 

 The resistance of the primary circuit, which contained a battery of 40 Btorage 

 cells, was 30 ohms. 



Figure 46 shows both reverse and direct curves for the magnet Q 

 when the primary and secondary coils were geometrically alike and 

 each had 1394 turns. The resistance of the primary circuit was about 

 16.7 ohm>. 



The curves of Figure 47 belong to a primary coil of 823 turns of the 

 magnet Q. The lines which have as origin represent currents of 

 about 2.05 amperesdue to a storage lottery of 10 cells ; the lines which 

 start at -V were caused by currents of 7.55 amperes from a battery of 

 40 '-ells. 



Figure 48 shows direct and reverse curves for a current of 3.30 am- 

 peres (due to a storage battery of 40 cells) in a coil of 1394 turns 



